In the field of graphic arts, an image-forming system giving high-contrast (in particular, higher than 10 in gamma) photographic characteristics are required for obtaining good reproduction of continuous tone images by dot images or good reproduction of line images.
Hitherto, for obtaining the aforesaid purposes, a specific developer called as "lithographic developer" has been used. The lithographic developer contains hydroquinone only as the developing agent and in the developer, a sulfite as preservatives is used as an adduct with formaldehyde and the concentration of free sulfite ion is very low (usually lower than 0.1 mole/liter) so that it does not hinder the infection developability. Thus, the lithographic developer is very liable to be air-oxidized and thus has a serious disadvantage that the developer cannot endure the storage thereof over 3 days.
As a process of using a stable developer capable of giving high-contrast photographic characteristics, there are processes of using hydrazine derivatives described in U.S. Pat. Nos. 4,224,401, 4,168,977, 4,166,742, 4,311,781, 4,272,606, 4,211,857, 4,243,739, etc. According to these processes, high-contrast and high-sensitive photographic characteristics are obtained and further since it is allowed to add a sulfite ion in a high concentration to the developer, the stability of the developer to air oxidation is greatly improved as compared with conventional lithographic developers.
On the other hand, for the light exposure of photographic light-sensitive materials, various light sources (e.g., light emitting diode (LED), He-Ne laser, Ar laser, etc.,) have been developed and realized. For giving the optimum spectral sensitivity to the spectral energy distribution of these light sources, it is necessary to select spectral sensitizing dye(s) and a system using a lithographic developer has hitherto been employed. That is, in the above-described image-forming system obtaining high-contrast photographic characteristics using a stable developer and a hydrazine derivative, the increase of sensitivity and contrast is accelerated and practical Dmax (below described) is realized by the use of a cationic compound as known up to the present (e.g., Japanese Patent Application Nos. 24,891/83, 9347/85, etc.,).
In this case, by using cationic dyes in the spectral sensitizing dyes, a higher practical Dmax is realized than the cases of using anionic dyes and betaine dyes.
However, in the above-described case, an undesirable phenomenon of the increase of so-called balck pepper, etc., simultaneously occurs, which becomes a serious problem in a photographic printing plate making.
Accordingly, various efforts have been paid for preventing the occurence of black peppers while keeping the high practical Dmax using cationic dyes as spectral sensitizing dyes.
Hitherto, as a means for preventing the occurence of black peppers, it has been proposed to reduce the amount of a hydrazine derivative but the means simultaneously causes the hindrance of the increase of sensitivity and contrast and is frequently accompanied by the reduction in gamma (.gamma.) and practical Dmax.
Therefore, a system capable of preventing the occurence of black peppers while keeping high practical Dmax and high sensitivity by the use of cationic dyes.